The main components in a vehicle drive train are drive unit and a transmission, whereby the transmission converts torque and rotational speed, so that the drive unit pull force of the vehicle is provided at the drive train output.
This present invention relates to a method of operating a drive train which comprises, beside the drive unit and the transmission, an all-wheel splitter, including an automated clutch, between the transmission and the drive train output. The automated clutch of the all-wheel splitter is particularly configured as an all-wheel multiple disc clutch.
The clutch in such an all-wheel splitter, being activated automatically, is operated in a continuous slip mode and splits a transmission output torque for achieving a variable torque distribution for the output axles in a way so that the transmission output torque, less a predetermined nominal torque value based on the all-wheel drive strategy, is transferred to a first drive axle, a so called main drive axle, and the output and the nominal torque to a second driven axle, the so called auxiliary axle, being transferred from the drive train. The all-wheel drive strategy, which sets the nominal torque and hereby the variable torque distribution between driven axles and the output, is implemented in a control unit of the drive train, preferably a transmission control unit.
Strict requirements are expected from an automatic operated clutch of an all-wheel splitter, i.e., positioning accuracy, positioning dynamics, and disengaging dynamics. Because of the constant and continuous slippage present at the clutch, or the constant rotational speed difference between the output driven axles and their allocated elements of the clutch, respectively, the all-wheel splitter clutch is exposed to a high thermal and mechanical stress, which result in wear and, therefore, cause malfunctions of the all-wheel splitter clutch.
So far, there are no known measures through which improper and high thermal stress of the clutch of the all-wheel splitter is reliably avoided. Therefore, there is a need for having a method of operating a drive train, through which its clutch is protected against a thermal overload.